Hollow tubular body for air intake duct, mold therefor, and method of molding the same

ABSTRACT

A polyamide resin containing reinforcing fiber is dry blended with a polyamide resin containing no or less reinforcing fiber. A polyamide resin containing 15 to 50% by weight of reinforcing fiber thus obtained is used as a material. By using a moving type core having a two-stage structure including a large diameter moving core and a small diameter moving core, a tubular hollow molded body  17  is formed, and redundant portions  18  and  19  are cut and removed.

TECHNICAL FIELD

The present invention relates to a hollow tubular body for an air intakeduct, and a mold and a molding method for the hollow tubular body, andmore particularly to a hollow tubular body for an air intake duct whichis suitable for a mechanical supercharger (hereinafter referred to as an“MSC” in this specification) that has been widely used for increasingthe volumetric efficiency of internal and external combustion engines ofan automobile or the like.

BACKGROUND ART

As resinous intake parts for internal and external combustion engines ofan automobile or the like, various ducts have been manufactured by blowmolding and an intake manifold has been manufactured by a fusibilitycore method or welding of a plurality of parts. However, they have notbeen resinified as an air intake duct for the MSC but have beenmanufactured by aluminum die casting using a sandmold.

If the sandmold is used, however, a product becomes very rough with amaximum surface roughness of Rz≧50μm and a mean surface roughness ofRa≈8 μm. For this reason, it is necessary to perform a grinding work inorder to keep a profile irregularity of a supercharger junction.Furthermore, a difference in level is easily caused by mismatch.Therefore, it is also necessary to perform a finishing work for a hosejunction.

The reasons why a resin has not been used for the air intake duct forthe MSC are as follows.

(1) It is hard to integrally mold a flange portion by the blow molding.

(2) Few resin materials for the blow molding have performance, forexample, strength, heat resistance and the like necessary for the airintake duct for the MSC. The resin materials having the performance suchas strength, heat resistance and the like are expensive. Moreover, thesurface roughness of an internal wall is deteriorated more than inexisting items (manufactured by the aluminum die casting).

(3) In the fusibility core method or the welding method of a pluralityof parts, the investment for a mold and initial plant should be madegreatly. In consideration of plant repayment, a cost is increased morethan in the existing items.

An injection molding method using a fused resin and a fluid such as aninert gas or the like together (a gas assist injection method which willbe hereinafter referred to as “GAI”) has recently been applied variouslyas a method for molding a hollow bent tube at a low cost.

The merits of the GAI are as follows: “(1) A mold can be manufactured bysimply adding comparatively inexpensive equipment to an ordinary moldfor injection molding; (2) Since a flange portion can be moldedintegrally and a mean surface roughness is small, a grinding work is notnecessary; (3) It is possible to select inexpensive resin materialssuitable for the present product from a great variety of injectionmolding resins; (4) It is possible to obtain appearance and dimensionalprecision equivalent to or more than those of an ordinary injectionmolded product; (5) A low pressure molding method is used so that thelife of the mold can be prolonged; and the like.”

However, the mere GAI has disadvantages, for example, “(1) If areinforcement (glass fiber or the like) is blended to such an extentthat necessary performance is revealed, an internal wall becomes roughin the same manner as in the blow molding; (2) It is hard to obtain thesame hollow rate as in existing items (manufactured by the aluminum diecasting); and the like.”

In consideration of these problems of the prior art, it is an object ofthe present invention to provide a hollow tubular body for an air intakeduct which can be manufactured at a low cost and has an excellentinternal smoothness. It is another object of the present invention toprovide a mold capable of stably molding a hollow tubular body for anair intake duct having various sizes and shapes, and a method formolding the hollow tubular body.

DISCLOSURE OF THE INVENTION

In order to attain the above-mentioned object of the present invention,a polyamide resin is selected as a thermoplastic resin. A polyamideresin blended with a proper quantity of reinforcing fiber and apolyamide resin blended with less or no reinforcing fiber are employedas a material. Furthermore, a mold for molding the resin materialincludes a cavity mold and a core mold. A moving type core having atwo-stage structure including a large diameter moving core and a smalldiameter moving core is provided in the core mold. Thus, theabove-mentioned object can be achieved.

The present invention provides a resinous hollow tubular body for an airintake duct which is molded by gas assist injection and integrallycommunicates from a flange to be coupled to a supercharger to a hosejunction by means of a bent tube portion and a straight tube portion,wherein a resin material is a polyamide resin containing 15 to 50 % byweight of reinforcing fiber.

It is preferable that a polyamide resin reinforced with fiber or thelike should be used because a balance of heat resistance, impactresistance and strength (tension, bending and compression) and a cost iskept. There are various kinds of polyamide resins in which 46 nylon, 11nylon and 12 nylon are expensive. Since the 46 nylon has a smalltemperature range for fusing and a time for obtaining a specific volumesuitable for GAI is short, it is hard to perform molding. Since the 11nylon and the 12 nylon have high fusing viscosities, a poor fluidity isobtained when suitable specific volumes are reached. Similarly, it ishard to perform molding. In this respect, polymetaxyleneadipamide, 66nylon and 6 nylon do not have such drawbacks. In particular, thepolymetaxyleneadipamide is an excellent resin material for the GAI.

Examples of the reinforcing fiber include glass fiber, carbon fiber,aramid fiber, a whisker-shaped reinforcement and the like. It ispreferable that the glass fiber should be used because a low cost isrequired and great reinforcing effects are obtained.

If the quantity of the reinforcing fiber to be added is less than 15% byweight, reinforcing effects cannot be obtained. If the quantity of thereinforcing fiber to be added is more than 50% by weight, a cost isincreased and moldability is deteriorated. The resin material isobtained by dry blending (A) a polyamide resin containing reinforcingfiber and (B) a polyamide resin containing no reinforcing fiber orcontaining less reinforcing fiber than in (A). If the resin material isused for fusing and mixing by the GAI, an island of the resin containingno (or less) reinforcing fiber is ununiformly floated in a sea of theresin containing the reinforcing fiber. If a pressurized fluid isinjected, the resin is expanded to envelop the reinforcing fiber.Consequently, the internal smoothness of a molded hollow tubular body isenhanced.

A bellows-shaped concavo-convex portion is provided on an outside of thebent tube portion that a pressurized fluid sent from the superchargerdirectly strikes, thereby partially changing a thickness. Consequently,it is possible to reduce resonance sounds made by causing the fluid sentfrom the supercharger to strike an internal wall of the hollow tubularbody.

Furthermore, if the hose junction is formed of a straight tube having alength of 30 mm or more, joining with a hose can conveniently beperformed.

The present invention provides a mold for molding a resinous hollowtubular body for an air intake duct which is molded by gas assistinjection and integrally communicates from a flange to be coupled to asupercharger to a hose junction by means of a bent tube portion and astraight tube portion, wherein a bent tubular cavity and a straighttubular cavity are formed in a cavity mold, a large diameter moving corewhich has the same shape and dimension as an opening of the flange to beformed by the bent tubular cavity and serves to move in a directionorthogonal to a flange face is provided in a core mold directlyconnected with the cavity mold, and a small diameter moving core to movein the same direction as the large diameter moving core is provided inthe large diameter moving core and serves to move after movement of thelarge diameter moving core is completed.

Furthermore, the present invention provides a method for molding ahollow tubular body for an air intake duct by a mold which directlyconnects a cavity mold forming a bent tubular cavity and a straighttubular cavity with a core mold having a large diameter moving core anda small diameter moving core, the method comprising the steps ofinjecting a fused resin into the cavity mold, injecting a pressurizedgas into the cavity to introduce the fused resin into the core mold,moving the large diameter moving core having the same shape anddimension as an opening of a flange to be formed by the bent tubularcavity in a direction orthogonal to a flange face, moving the smalldiameter moving core provided in the large diameter moving core in thesame direction as the large diameter moving core after movement of thelarge diameter moving core is completed, performing cooling, andremoving a redundant portion formed by a resin injection portion and themoving core from the hollow tubular body obtained after getting out ofthe mold.

According to the mold having the above-mentioned structure and themolding method, if the pressurized gas is injected into the fused resinmaterial introduced into the cavity mold, the resin material is reducedin a thickness while being pushed toward the internal surface of themold by the pressure of the pressurized gas. In some cases, a thickportion is formed on the tip of the resin flowing in the cavity.However, the moving type core is provided on the tip of the flowingresin where the thick portion is easily formed. The moving type core hasa two-stage structure including the large diameter moving core having alarge sectional area and the small diameter moving core having a smallsectional area. Therefore, in a case where the thick portion is formedeven if the large diameter moving core is moved to a terminal position,the small diameter moving core in the large diameter moving core ismoved to the terminal position so that a new cavity is formed. Bydrawing the thick portion into the cavity, it is possible to obtain ahollow tubular body having an almost uniform thickness as a whole.

In a case where an end face provided on the hose junction side of thehollow tubular body is set as a starting point and an end face providedon the flange side is set as an end point, end faces of the largediameter moving core and the small diameter moving core on the flangeside are gradually inclined inwardly apart from the flange by setting acontact point with the flange as an origin in such a manner that adistance between the starting point and the end point is almostconstant. Consequently, a local difference in a thickness is not made onthe hollow tubular body. Therefore, the hollow tubular body is brokenwith difficulty during the molding.

The present invention having the above-mentioned structure can provide ahollow tubular body for an air intake duct having an excellent internalsmoothness and a uniform thickness at a low cost. According to the moldand the molding method of the present invention, a hollow tubular bodyfor an air intake duct having various sizes and shapes can be stablymolded without breaking a resin wall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a mold according to the present invention;

FIG. 2 is an elevational view showing the mold according to the presentinvention;

FIG. 3 is a side view showing a tubular hollow molded body formed by amold according to an embodiment of the present invention;

FIG. 4A is a side view showing an air intake duct obtained by a methodaccording to an embodiment of the present invention, and

FIG. 4B is a view seen in an X direction in FIG. 4A; and

FIG. 5 is a front view showing the air intake duct obtained by themethod according to the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below. A resinmaterial to be used was obtained by dry blending, at a weight ratio of1:1, “Reny6002 (containing no glass fiber)” and “Reny1032 (containing60% by weight of glass fiber)” manufactured by Mitsubishi EngineeringPlastic Co., Ltd. The dry blended resin was injected into a mold shownin FIGS. 1 and 2 using a GAI unit manufactured by Nireko Co., Ltd.,thereby molding a hollow tubular body.

With reference to FIGS. 1 and 2, the reference numeral 1 denotes amolding plate, the reference numerals 2, 3, 4 and 5 denote inserts 1, 2,3 and 4, respectively, the reference numeral 6 denotes a resin inlet,the reference numeral 7 denotes a pressurized gas inlet, the referencenumeral 8 denotes a guide pin, the reference numeral 9 denotes abar-shaped runner, the reference numeral 10 denotes a horn-shapedrunner, the reference numeral 11 denotes a straight tubular cavity, andthe reference numeral 12 denotes a bent tubular cavity. A bellows-shapedconcavo-convex portion 12 a is formed on an outside of the bent tubularcavity 12. The reference numeral 13 denotes a large diameter movingcore, and the reference numeral 14 denotes a small diameter moving core.End faces E of the large diameter moving core 13 and the small diametermoving core 14 on a flange side are gradually inclined inwardly apartfrom a flange 15 by setting a contact point with the flange 15 as anorigin. The large diameter moving core 13 is movable between points Aand B, and the small diameter moving core 14 is movable between points Cand D. The reference numeral 16 denotes a rod of a hydraulic cylinderfor the movement of the moving core.

The fused resin material was injected into the resin inlet 6 of the moldhaving the above-mentioned structure, and a pressurized gas was theninjected through the pressurized gas inlet 7. Consequently, the resinmaterial formed a hollow portion while being expanded by the pressure ofthe pressurized gas. When the flowing tip of the resin reached themoving core, the large diameter moving core 13 moved left together withthe small diameter moving core 14 and pushed the resin against anexternal wall where the large diameter moving core 13 had moved.Finally, a terminal position B was reached. Thus, a hollow tubular bodyhaving an almost uniform thickness could be molded (first to sixthembodiments in the following Table 1).

As another embodiment, the above-mentioned steps were performed from theinjection of the fused resin material till the movement of the largediameter moving core 13 to the terminal position B. Then, thepressurized gas was further injected through the pressurized gas inlet7. Consequently, the small diameter moving core 14 moved left in thelarge diameter moving core 13 stopped at the terminal position B. Inparticular, the resin in the flowing tip which easily forms a thickportion was drawn into the movement trace of the small diameter movingcore 14 to reach a terminal position D. Thus, a tubular hollow moldedbody 17 having an almost uniform thickness shown in FIG. 3 could beobtained (seventh to twelfth embodiments in the following Table 1).

For comparison, the mold including a moving core having a horizontal endface was used. Similarly, a tubular hollow molded body was obtained(comparative examples 1 to 6 in the following Table 1).

Redundant portions 18 and 19 were cut and removed from the tubularhollow molded body 17 shown in FIG. 3. Consequently, a hollow tubularbody 20 for an air intake duct shown in FIGS. 4 and 5 was obtained.

The results of a molding test for the above-mentioned tubular hollowmolded body will be listed in the following Table 1.

TABLE 1 Gas injec- Area of top Support pre- Breakage of Resin injec-tion delay Gas injec- Type of mov- panel of mov- Capacity of sure ofresin wall of Ra Rz tion time time tion time ing core ing core movingcore moving core moving core μm μm Embodiment 1 2 seconds 1 second 4seconds Inclination 24.5 cm² 85.5 cm³ 118 kg/cm²  Not broken 2.5 24 type2 ↑ ↑ ↑ ↑ ↑ ↑ 59 kg/cm² ↑ ↑ ↑ 3 ↑ ↑ ↑ ↑ ↑ ↑ 20 kg/cm² ↑ ↑ ↑ 4 6 seconds2 seconds ↑ ↑ ↑ ↑ 118 kg/cm²  ↑ 5.0 35 5 ↑ ↑ ↑ ↑ ↑ ↑ 59 kg/cm² ↑ ↑ ↑ 6 ↑↑ ↑ ↑ ↑ ↑ 20 kg/cm² ↑ ↑ ↑ 7 2 seconds 1 second ↑ ↑ ↑ 93.5 cm³ 118kg/cm²  ↑ 2.5 20 8 ↑ ↑ ↑ ↑ ↑ ↑ 59 kg/cm² ↑ ↑ ↑ 9 ↑ ↑ ↑ ↑ ↑ ↑ 20 kg/cm² ↑↑ ↑ 10 6 seconds 2 seconds ↑ ↑ ↑ ↑ 118 kg/cm²  ↑ 5.0 35 11 ↑ ↑ ↑ ↑ ↑ ↑59 kg/cm² ↑ ↑ ↑ 12 ↑ ↑ ↑ ↑ ↑ ↑ 20 kg/cm² ↑ ↑ ↑ Comparative 1 2 seconds 1second ↑ Horizontal 20.5 cm² 92.0 cm³ 118 kg/cm²  Broken 3.0 24 exampletype 2 ↑ ↑ ↑ ↑ ↑ ↑ 59 kg/cm² ↑ ↑ ↑ 3 ↑ ↑ ↑ ↑ ↑ ↑ 20 kg/cm² ↑ ↑ ↑ 4 6seconds 2 seconds ↑ ↑ ↑ ↑ 118 kg/cm²  ↑ 5.2 40 5 ↑ ↑ ↑ ↑ ↑ ↑ 59 kg/cm² ↑↑ ↑ 6 ↑ ↑ ↑ ↑ ↑ ↑ 20 kg/cm² ↑ ↑ ↑

The following respects are obvious from the Table 1.

(1) The resin wall was not broken over the hollow tubular body accordingto the first to twelfth embodiments.

(2) The resin wall of the moving core portion was broken over the hollowtubular body according to the comparative examples 1 to 6. After cuttingthis portion, therefore, an opening shape became distorted.Consequently, working man-day was increased before a product wasoffered.

(3) In the first to third embodiments, the seventh to ninth embodimentsand the comparative examples 1 to 3, a time for injecting the resin isshort, i.e., 2 seconds. A hollow portion is formed with a low viscosityof the fused resin when the injection is completed. Therefore, adeflection in thickness is increased by a counterflow of the resin sentfrom the moving core. However, the counterflow of the resin could beprevented by cooling the moving core down to 60° C. or less at a coldblast.

(4) In the first to third embodiments, the seventh to ninth embodimentsand the comparative examples 1 to 3, the time for injecting the resin isshort, i.e., 2 seconds, and the viscosity of the fused resin is low whenthe injection is completed. Therefore, the obtained molded product has asmall surface roughness.

In the fourth to sixth embodiments, the tenth to twelfth embodiments andthe comparative examples 4 to 6, however, the time for injecting theresin is long, i.e., 6 seconds, and the viscosity of the fused resin ishigh when the injection is completed. Therefore, the obtained moldedproduct has a slightly great surface roughness.

INDUSTRIAL AVAILABILITY

Since the present invention has the above-mentioned structure, it issuitable for a device for stably molding a hollow tubular body for anair intake duct having various sizes and shapes which has an excellentinternal smoothness at a low cost.

What is claimed is:
 1. A resinous hollow tubular body for an air intakeduct which is molded by gas assist injection and integrally communicatesfrom a flange to be coupled to a supercharger to a hose junction bymeans of a bent tube portion and a straight tube portion, wherein aresin material is a polyamide resin containing 15 to 50% by weight ofreinforcing fiber.
 2. The hollow tubular body for an air intake ductaccording to claim 1, wherein the polyamide resin ispolymethaxyleneadipamide, and the reinforcing fiber is glass fiber. 3.The hollow tubular body for an air intake duct according to claim 1,wherein the resin material is obtained by dry blending a polyamide resincontaining reinforcing fiber and a polyamide resin containing no or lessreinforcing fiber.
 4. The hollow tubular body for an air intake ductaccording to claim 1, 2 or 3, wherein a bellows-shaped concavo-convexportion is provided on an outside of the bent tube portion that apressurized fluid sent from the supercharger directly strikes.
 5. Thehollow tubular body for an air intake duct according to claim 1, 2 or 3,wherein the hose junction is formed of a straight tube having a lengthof 30 mm or more.
 6. A mold for molding a resinous hollow tubular bodyfor an air intake duct which is molded by gas assist injection andintegrally communicates from a flange to be coupled to a supercharger toa hose junction by means of a bent tube portion and a straight tubeportion, wherein a bent tubular cavity and a straight tubular cavity areformed in a cavity mold, a large diameter moving core which has the sameshape and dimension as an opening of the flange to be formed by the benttubular cavity and serves to move in a direction orthogonal to a flangeface is provided in a core mold directly connected with the cavity mold,and a small diameter moving core to move in the same direction as thelarge diameter moving core is provided in the large diameter moving coreand serves to move after movement of the large diameter moving core iscompleted.
 7. The mold for molding a hollow tubular body for an airintake duct according to claim 6, wherein in a case where an end faceprovided on a hose junction side of the hollow tubular body is set as astarting point and an end face provided on a flange side is set as anend point, end faces of the large diameter moving core and the smalldiameter moving core on the flange side are gradually inclined inwardlyapart from the flange by setting a contact point with the flange as anorigin in such a manner that a distance between any circumferentialpoint of the end face provided on the hose junction side and the endpoint is almost constant.
 8. A method for molding a hollow tubular bodyfor an air intake duct by a mold which directly connects a cavity moldforming a bent tubular cavity and a straight tubular cavity with a coremold having a large diameter moving core and a small diameter movingcore, the method comprising the steps of: injecting a fused resin intothe cavity mold; injecting a pressurized gas into the cavity tointroduce the fused resin into the core mold; moving the large diametermoving core having the same shape and dimension as an opening of aflange to be formed by the bent tubular cavity in a direction orthogonalto a flange face; moving the small diameter moving core provided in thelarge diameter moving core in the same direction as the large diametermoving core after movement of the large diameter moving core iscompleted; performing cooling; and removing a redundant portion formedby a resin injection portion and the moving core from the hollow tubularbody obtained after getting out of the mold.